My long-term objective is to understand the molecular mechanisms that underlie the balance between growth and differentiation in mammalian epidermis and its appendages. The knowledge of factors controlling this balance is prerequisite to understanding how this equilibrium goes awry in human skin cancers and genetic disorders. A search for such factors resulted in the identification of basonuclin (bsn), a protein that is selectively expressed in the dividing cells of epidermis and hair follicles. In this proposals, the role of bsn in epidermis will be studied further. Specifically, I propose to: (1) explore the possible functions of bsn by using gene targeting to ablate bsn expression in mice; this will be done using the Cre-Lox system. (2) Examine how misappropriate expression of bsn alters the program of growth and/or differentiation in epidermis and its appendages, this will be achieved using a differentiating keratinocyte-specific promoter to target expression of bsn-gene to differentiating keratinocytes of transgenic mice. (3) Clone and characterize differences that arise from ablation of the bsn-gene in mouse epidermis or in keratinocytes cultured from these mice; once the earliest changes have been detected, subtractive hybridization methods will be used to clone these molecular differences. (4) Assess whether bsn is a DNA binding protein and ascertain the possible downstream targets for this protein.